Treatment of skin with lasers have been the subject of study since the early 1960s. A variety of lasers have been used in dermatologic practice. Different lasers are primarily distinguished by a wavelength of the light produced, measured in nanometers, such as the XeF excimer (351 nm), argon (488 nm, 514 nm), ruby (694 nm), Nd:YAG (1060 nm), and CO.sub.2 (10,600 nm) lasers.
Photothermolysis of skin has been demonstrated using dye laser pulses and Q-switched ruby laser pulses. It has been found that radiation from Q-switched ruby lasers deeply penetrates the epidermis and dermis. It has also been found that application of ruby red laser energy can cause depigmentation of the skin as well as significant follicular damage to the extent that the hair will fall out.
The Q-switched ruby laser has been used for the treatment of tattoos, pigmented lesions, and conventional ruby lasers have been used to treat epidermal and dermal pigmented lesions. Studies based on experimentation with Q-switched ruby lasers, as well as other lasers, have reported skin depigmentation and temporary hair loss.
The use of lasers for non-invasive hair removal has been disclosed in U.S. Pat. No. 5,059,192, issued Oct. 22, 1991 to Nardo Zaias, entitled METHOD OF HAIR DEPILATION. This patent teaches the use of a pulsed ruby laser as the preferred embodiment. The ruby laser radiation (694 nm wavelength) penetrates deep into tissue and is relatively well absorbed by melanin to cause thermal damage to dark, melanin rich hair shafts and follicles.
U.S. Pat. No. 5,226,907, issued Jul. 13, 1993 to Nikoli Tankovich, entitled HAIR REMOVAL DEVICE AND METHOD and U.S. Pat. No. 5,425,728, issued Jun. 20, 1995 to Nikoli Tankovich, entitled HAIR REMOVAL AND METHOD teach the use of a CO.sub.2 pulse laser and a Nd:YAG laser, among other types of lasers, to effect hair removal in conjunction with light absorbing oil used to stain hair.
The Nd:YAG laser is limited to relatively low energy levels at affordable commercial production costs. It is effective only for highly absorptive hairs, usually stained for this purpose. Energy levels adequate for hair removal with bare hairs makes it impractical to use an Nd:YAG laser.
Large pulsed ruby lasers are capable of delivering very high energy levels--as high as 40 J. As a result, they can attain the energy fluences of 15-70 J/cm.sup.2 necessary for hair removal. However, ruby lasers can be fired only at a very low repetition rate--approximately 1 pulse per second (pps). This limits the benefit of using a scanner such as that described in U.S. Pat. No. 5,411,502 to Eliezer Zair and the computerized pulsed generator (CPG) scanner, commercially available from Coherent Inc. of California, USA. This low repetition rate is too low to cover large treated areas as legs and hands in a reasonable time. A 10.times.30 cm.sup.2 area (one leg) would require some 1200 pulses, each pulse covering an area of 0.25 cm.sup.2 (typical for hair removal with a 5 Joules laser). Assuming a repetition rate of 1 pps, this leads to 20 minutes for a single leg, or over 1 hour for two legs and two hands. This considerably limits the number of patients treatable for hair removal with the expensive laser.
Another drawback of pulsed ruby lasers is their limited pulse time duration. Ruby lasers operated in their free running modes can usually attain a maximum time duration of 300-1000 microseconds. Extending the pulse duration to 1-10 milliseconds is almost impractical. On the other hand, it would be desirable to operate ruby lasers at pulse durations of 1-10 milliseconds in most cases of hair removal because of hair follicle diameters being of over 100 microns.
A third drawback of ruby lasers is their size due to their low efficacy. A 5 Joules, 1 pps ruby laser may typically be of 150 cm.times.70 cm.times.70 cm size. A 25 Joule laser may weigh over 400 kilograms.
U.S. Pat. No. 5,290,273, issued Mar. 1, 1994 to Oon Tan, entitled LASER TREATMENT METHOD FOR REMOVING PIGMENT CONTAINING LESIONS FROM THE SKIN OF A LIVING HUMAN and U.S. Pat. No. 5,217,455, issued Jun. 9, 1993 to Oon Tan, entitled LASER TREATMENT METHOD FOR REMOVING PIGMENTATIONS, LESIONS, AND ABNORMALITIES FROM THE SKIN OF A LIVING PERSON, teach the use of an Alexandrite laser instead of a ruby laser to treat pigmentation, lesions and skin abnormalities. Both teach that before and after irradiation, the area irradiated should be checked for the presence or absence of adhexac (skin appendages) such as hairs. If a hair loss condition is observed, then the energy density from the laser radiation should be decreased for subsequent treatments. The pulse duration is 10-300 nanoseconds.
Skin treatment employing laser based systems, usually pulsed laser based systems is well known in the art. Such laser based systems are used inter alia for cutaneous vascular lesions treatment and for hair removal, the latter application being described for example in U.S. Pat. Nos. 5,059,192 to Zais and 5,226,907 to Tankovich.
As is also well known in the art, the operation of laser based systems for cutaneous treatment is more effective when the tissue is cooled. Examples for prior art devices for cooling the skin during laser treatment are U.S. Pat. No. 5,057,104, U.S. Pat. No. 5,282,797 and U.S. Pat. No. 5,486,172 to Chess specifically designed for cutaneous vascular lesions treatments and U.S. Pat. No. 5,344,418 to Ghaffari.
A major disadvantage of prior art laser based systems for cutaneous treatment is that the operation of the laser is not visible to the physician carrying the treatment, thus he can not be sure that the laser covered the entire area to be treated. This results in an inhomogeneous treatment of the skin, such as an inhomogeneous removal of hair from the patient skin in the case of hair removal treatment.